In the art, handover (HO) of a mobile terminal from a serving cell to a neighbouring cell when channel quality is commonly performed. This is typically performed when channel quality for an ongoing data session or call in the serving cell becomes too poor, in which case the call or session is transferred to the neighbouring cell. The mobile terminal is typically a User Equipment (UE) such as a mobile phone, a personal digital assistant (PDA), a smart phone, a tablet, a laptop, a media player, etc.
Handover may be undertaken from a serving cell to a neighbouring cell employing the same Radio Access Technology (RAT), for instance via Evolved Universal Terrestrial Radio Access Network (E-UTRAN) in case of Long Term Evolution (LTE) communication. This is referred to as intra-RAT handover. Alternatively, handover may be undertaken from a serving cell to a neighbouring cell employing different RATs, for instance from E-UTRAN to Universal Terrestrial Radio Access Network (UTRAN) in case of Universal Mobile Telecommunication System (UMTS) communication or even to a non-3rd Generation Partnership Project (3GPP) technology such as Wireless Local Area Network (WLAN). This is referred to as inter-RAT handover.
In a typical wireless communications network, a network node such as a base station may serve many cells and each cell typically only covers a limited geographical area with some overlap; therefore, handover becomes a very important feature for the seamless mobility of UEs in the entire wireless communications network. The performance of handover also becomes an important factor that affects the user's experience and the amount of radio resources used for the connection. One main purpose of handover is to make sure the UE connection is always maintained by being served by the best frequency and cell. This requires continuous measurements of properties indicating cell capacity of the serving and neighbouring cells.
Another field requiring extensive cell measurements is downlink scheduling, where resources are scheduled/allocated to UEs for maximization of system throughput while maintaining agreed QoS contracts. In order for a scheduler at a base station to arrive at adequate scheduling decisions, the scheduler should ideally be aware of channel quality of all the UEs in the system. This results in extensive signalling.
In an example, when effecting inter-frequency/inter-RAT handover, the UE continuously measures quality of a channel established with a base station (referred to as an eNodeB in an LTE network) of the currently serving cell. In case a so called A2 event occurs in LTE, i.e. a value of a property of a channel established with the serving cell as measured by the UE falls below a predetermined quality threshold value, the UE responds with sending a measurement report accordingly to the eNodeB indicating that the quality of the serving cell has fallen below the threshold value.
The eNodeB will in its turn initiate a measurement of the quality of inter-frequency or inter-RAT neighbouring candidate cells to which the UE can be handed over. Thus, the eNodeB sends a Radio Resource Control (RRC) Connection Reconfiguration message thereby triggering a so called B5 event, i.e. instructing the UE to measure channel quality of the candidate cell(s) to determine if a value of a property of a channel established with the candidate cell is above a predetermined quality threshold value for the candidate cell. The UE will send a further report to the eNodeB regarding the quality of the candidate cell(s), on the basis of which further report the eNodeB will determine if and to which candidate cell the UE should be handed over.
This current approach of determining whether to handover the UE causes latency in the handover procedure, and further requires a great deal of signaling between the eNodeB and the UE.